Extreme Acidic Conditions Research Articles

Physicochemical and functional characteristics of proteins treated by a pH‐shift process: a review

SummaryAdvanced structures of food proteins are maintained by many forces such as hydrophobic activities, electrostatic interaction, and disulphide bond interaction, which can affect their functional characteristics to a certain extent. Therefore, many approaches have been utilised to improve functional characteristics of food proteins. pH‐shift process refers to the method that food proteins are treated under extreme alkaline or acid conditions followed by adjusting pH to isoelectric point or neutral pH. Many studies have showed that pH‐shift process can significantly affect the functional characteristics of food proteins, for example emulsifying activities, forming property, solubility and water/oil adsorption ability. pH‐shift process has been utilised to recover protein isolates from many sources including fish, fish by‐products, meat processing products. Many researches have indicated that the functional and physicochemical characteristics of recovered protein isolates are significantly influenced by pH‐shift process. In this paper, the latest studies regarding the functional and physicochemical characteristics of proteins treated or recovered through pH‐shift process, and potential applications of obtained protein isolates in the production of the hydrolysates or used as a delivery system were reviewed.

On the long-term pH stability of polyelectrolyte multilayer nanofiltration membranes

Long-term pH stability is critical for nanofiltration membranes in many applications, e.g. dairy and mining industry. We present a systematic study on the long-term pH stability of four different polyelectrolyte multilayer (PEM) nanofiltration membranes. The stability was assessed by comparing their performance before and after exposure to up to 1 M HNO3 (~pH 0) and 1 M NaOH (~pH 14), in terms of pure water permeance (PWP), salt retention, and molecular weight cut-off (MWCO).Poly(diallyldimethylammonium chloride) (PDADMAC)/poly(styrenesulfonate) (PSS) nanofiltration membranes show excellent stability under extreme acidic and basic conditions for more than 2 months (10.7 L m−2h−1bar−1 PWP, 95.5% MgSO4 retention, 279 g mol−1 MWCO), attributed to the use of strong polyelectrolytes, of which the charge is unaffected by pH. Poly(allylamine hydrochloride) (PAH)/PSS membranes show stable performance when exposed to extreme acidic conditions (9.7 L m−2h−1bar−1 PWP, 97.5% MgSO4 retention, 249 g mol−1 MWCO). Under these conditions, PAH remains charged and therefore a stable multilayer is maintained. PDADMAC/poly(acrylic acid) (PAA) and PAH/PAA membranes are not stable at extreme pH conditions.These results highlight that PEM nanofiltration membranes, especially PDADMAC/PSS membranes, have tremendous potential for use at extreme pH conditions. Compared to most commercially available membranes they have superior long-term stability and very relevant performance.

Computationally Designed Perrhenate Ion Imprinted Polymers for Selective Trapping of Rhenium Ions

Computationally designed ion imprinted polymers (IIP) were synthesised for selective binding of perrhenate ion from CMSX-4 superalloy leach solutions. A library of functional monomers was screened using Density Functional Theory (DFT) based on their binding energy with perrhenate ion. DFT calculations were also employed to determine the template:monomer ratio of 1:2 from binding energy calculation of the complex formed, and perrhenate ion formed the most stable complex with protonated 4-vinylpyridine (4VP) at 1:2 molecular ratio. An optimum imprinting ratio of 2:4:40 for the functional monomer:cross-linker:perrhenate ion template was calculated using molecular dynamics simulation of a fixed number of component molecules in a periodic boundary and isothermal conditions (NVT-Molecular Dynamics) using MM+ force field. The perrhenate ion selective IIPs were synthesised via bulk polymerisation and combinatorial screening of the imprinting porogen composition was employed to compliment the computational screening. The resulted IIPs showed fast kinetics, high binding capacity (122 mg Re/g polymer), and adsorption processes governed by pseudo-second order kinetics. The IIP synthesised using 4-vinylpyridine and ethylene glycol dimethylacrylate (EGDMA) show superior selectivity towards perrhenate ion in the presence of the oxides, hydroxides, and chlorides of Al, Co, Cr, Hf, Mo, Ni, Ta, Ti, and W in the feed leach solution at pH = 7.0. The perrhenate ion IIPs demonstrated excellent chemical and physical stability towards extreme acidic stripping conditions, and storage for an extended period. Therefore, the use of perrhenate ion imprinted polymers for separation as part of the industrial recycling of rhenium from superalloy leach solutions is recommended.

Spiro N-oxidized pyrrolidone-appended hemicyanine: Synthesis, lower pH-sensing and colormetric temperature sensing

Three novel spiro N-oxidized pyrrolidone-appended hemicyanine derivatives have been synthesized and characterized by 1H NMR, 13C NMR, UV–Vis and HRMS. The molecular structures of spirocyclic dye 2a and its opening-ring product 2aa have been determined by single-crystal X-ray diffraction analysis. The UV–vis spectra show significant solvatochromic behavior of three spirocyclic derivatives, especially in acidic and alkaline solvents. Spirocyclic dye 2a displays an excellent pH dependent behavior and responds linearly to extreme acidic conditions in the pH ranges of 1-4. The absorption spectra studies on opening-ring reaction reveal that acid and heat dual stimulation can induce opening-ring of 2a, which exhibits temperature-responsive linear in the range of 25–45 °C, behaving a colorimetric thermometer sensing. These properties provide the possibility for 2a-c to be used as stimulating response molecule switch.

Polysulfonamide coating layer polymerized by1,3-disulfonyl chloride and polyethylenimine to achieve acid resistant TFC membranes

In this work polysulfonamide membranes are presented that are prepared by the interfacial polymerization of polyethylenimine (PEI) and benzene-1,3-disulfonyl chloride (BDSC) on porous polyvinylidenefluorid support membrane. The thin film composite (TFC) polysulfonamide membranes show superior acid stability as compared to conventional polysulfonamide membranes that are derived from monomeric amine and benzene-1,3-disulfonyl chloride. The polysulfonamide membranes show exceptionally strong resistance towards nucleophilic attack induced by extreme acidic conditions. This is verified by the dyes rejection performance in 20%(w/v) H2SO4 and 2.5%(w/v) HNO3 aqueous solution at 70 ± 5 °C for 24 h. PEI-PSA and PEI/PIP-PSA membranes were considerably stable in two acids. In contrast, the durability of PEI/MPD-PSA was lower than the other two. The changes in CV and MO dye rejection were −3.15% and −2.19%, and −1.11%, −5.6% for PEI-PSA and PEI/PIP-PSA, respectively after H2SO4 soaking while they were −20% and −15.9% for PEI/MPD-PSA. Moreover, the changes in CV and MO dye rejection were −15.7% and −14.3%, and −7.8%, −5.7 % for PEI-PSA and PEI/PIP-PSA, respectively after HNO3 soaking while they were −17.7% and −10.2% for PEI/MPD-PSA.

Distinct roles of salt cations and anions upon the salting-out of electro-positive albumin

Precipitation experiments of electro-positive albumin by the action of a wide number of salts, and at different concentrations, were performed at a constant temperature (25 °C). The pH range studied covered extreme acidic conditions up to hydronium concentrations where the dissociation of the protein carboxyl groups becomes noticeable. The time required for the clouding phenomenon to occur and the quantity of salted-out protein were also ascertained. The results here reported show that the salt anion is the main salting-out species for the positively charged protein, where their efficacy in salting-out albumin from aqueous solution increases in the order: F− < Cl− < Br− < NO3− < I− < SCN− ~ ClO4− < SO42−. Although at extreme pH conditions the salt cation has no significant influence on the protein salting-out, experiments performed at higher pH values, where the carboxyl groups starts to dissociate, revealed a non-monotonic effect of the salt upon protein precipitation. We interpret this observation as a result of the presence of different protein forms, with which the salt cation participates in chemical equilibrium. Overall, the proteins salting-out phenomenon induced by salt can be rationalized by a general mechanism driven by electrostatic interactions and chemical equilibrium concepts.

Operational parameters in H2S biofiltration under extreme acid conditions: performance, biomass control, and CO2 consumption.

This paper reports the treatment of gaseous hydrogen sulfide, H2S, in a biotrickling filter (BTF) under extreme acidic pH conditions (≈ 1.2). The effect of adding thiosulfate (Na2S2O3.5H2O) to promote biomass growth, feeding low concentrations of ozone to control excess biomass, and the carbon dioxide, CO2, consumption by the chemolithoautotrophic consortium were evaluated. The results showed a global removal efficiency over 98.0% with loads of H2S > 50 g m-3 h-1 (at 639 ppmv) and a linear relation between H2S elimination capacity with the CO2 consumption rate of around 0.1 gCO2/gH2S. Supplementing sulfur in the medium with 2 g L-1 thiosulfate resulted in negative effect performance. Respirometry tests proved that the consortium could not utilize this sulfur form at this pH. Additionally, continuous and intermittent O3 feeding to the BTF in gaseous concentrations of 98 ± 5.4 mg m-3 caused a slight decreased in the performance but the biomass activity in the BTF was only slightly affected allowing a quick performance recovery once O3 addition was suspended.

Cheap, reliable, reusable, thermally and chemically stable fluorinated hexagonal boron nitride nanosheets coated Au nanoparticles substrate for surface enhanced Raman spectroscopy

In this study, multi-layered fluorinated hexagonal boron nitride nano-sheets (F-BN) coated gold-nanoparticles (AuNPs/glass) SERS-active substrate is presented. Thermal and chemical stabilities with reusability tests of F-BN/AuNPs/glass SERS-active substrate were performed. The AuNPs on glass substrate (AuNPs/glass) was first prepared by combining ion-sputtering technique with a rapid annealing treatment. Second step involved the spin coating of a thin film of F-BN as a shielding layer on AuNPs/glass substrate. It was seen that Raman performance of FBN/AuNPs/glass substrate is more stable and efficient as compared to bare AuNPs/glass substrate under strong chemical and oxidative environments. Moreover, outcome of cycle tests indicated that F-BN as a protecting layer, could recover the long-term stability of the bare AuNPs/glass SERS-active substrate. DFT based calculations were also performed and theory supported our experimental results that R6G on F-BN/glass has higher adsorption capability as compared to BN/glass. Consequently, our proposed multi-layered F-BN is found to be an excellent wrapping material on AuNPs/glass substrate for cost effective production and reliable fabrication of capable SERS. It is also useful for the detection of particular sensing molecules at high temperatures or in extreme acidic conditions that are too complicated to be analyzed by means of conventional SERS. Hence, our proposed method will promote the wider usage of functionalized BN/metal based SERS in multidisciplinary fields.

Effect of cement incorporation on the leaching characteristics of elements from fly ash and slag treated soils

Inclusion of cement in fly ash and slag mixed soils could potentially alter the leaching behavior of elements. This study investigated the leaching characteristics of calcium (Ca), magnesium (Mg), sulfur (S), manganese (Mn), barium (Ba) and chromium (Cr) from cement activated soil-fly ash, soil-slag mixtures and soil, fly ash, steel slag and cement alone. Batch water leach tests, acid neutralization capacity and pH-dependent leach tests were performed. Test results indicated that, effluent concentrations of Ca and Ba increased, while Mg concentrations decreased with cement additions. No consistent trend was observed between S concentrations and cement content. The leaching of Cr and Mn remained unaffected by cement incorporation. Results of this study showed that the solution pH had the greatest influence on the leaching behaviors of the elements. Ca, Mg, S and Mn followed cationic leaching patterns, whereas Ba showed both cationic and amphoteric leaching patterns. The highest concentrations of Cr were observed at extreme acidic conditions, followed by a concentration plateau at the pH range of 5.5–10, and subsequent decrease and increase in concentrations at pH of 11.5 and 13, respectively. Geochemical modeling results suggested that except for Cr, the leaching mechanisms of the elements were controlled by their sulfate and (hydr)oxide minerals. The leaching of Cr was possibly controlled by BaCrO4 and CaCrO4. It was observed that the presence of carbonate minerals did not play a significant role on the leaching mechanisms of the elements, when cement was used as an activator.

PH-Dependent Thermal Stability of Vibrio cholerae L-asparaginase.

pH is one of the decisive macromolecular properties of proteins that significantly affects enzyme structure, stability and reaction rate. Change in pH may protonate or deprotonate the side group of aminoacid residues in the protein, thereby resulting in changes in chemical and structural features. Hence studies on the kinetics of enzyme deactivation by pH are important for assessing the bio-functionality of industrial enzymes. L-asparaginase is one such important enzyme that has potent applications in cancer therapy and food industry. The objective of the study is to understand and analyze the influence of pH on deactivation and stability of Vibrio cholerae L-asparaginase. Kinetic studies were conducted to analyze the effect of pH on stability and deactivation of Vibrio cholerae L-asparaginase. Circular Dichroism (CD) and Differential Scanning Calorimetry (DSC) studies have been carried out to understand the pH-dependent conformational changes in the secondary structure of V. cholerae L-asparaginase. The enzyme was found to be least stable at extreme acidic conditions (pH< 4.5) and exhibited a gradual increase in melting temperature from 40 to 81 °C within pH range of 4.0 to 7.0. Thermodynamic properties of protein were estimated and at pH 7.0 the protein exhibited ΔG37of 26.31 kcal mole-1, ΔH of 204.27 kcal mole-1 and ΔS of 574.06 cal mole-1 K-1. The stability and thermodynamic analysis revealed that V. cholerae L-asparaginase was highly stable over a wide range of pH, with the highest stability in the pH range of 5.0-7.0.

Relationship between Degree of Polymeric Ionisation and Hydrolytic Degradation of Eudragit® E Polymers under Extreme Acid Conditions.

The commercial copolymers Eudragit® E 100 and Eudragit® PO are widely used materials in the pharmaceutical field as coating systems. Such materials derived from amino-methacrylate groups under acidulated conditions may acquire an ionisable fraction or undergo hydrolytic degradation of the polymeric structure. This work focused on establishing the chemical, physical, and surface changes of two reprocessed polymeric materials, here named as EuCl-E-100 and EuCl-E-PO, which were obtained from the commercial Eudragit® E 100 and Eudragit® E PO, respectively. The commercial materials were exposed to extreme acid conditions, where the polymers were solubilised and subsequently dried by the refractance window method. The materials obtained were chemically characterised by potentiometric titration, nuclear magnetic resonance spectroscopy (1H NMR and 13C NMR) in one and two dimensions (COSY, HSQC, and HMBC), infrared spectroscopy, X-ray diffraction, and differential scanning calorimetry. Changes in the physical properties of the materials were evaluated through studies of flowability, compactability, and their ability to gain and lose humidity. Surface thermodynamic studies were carried out through contact angle measurements using the sessile drop method. The results showed that the processed polymeric materials acquired a substantial degree of ionisation without undergoing hydrolysis of the esterified groups. Furthermore, such changes improved the flow characteristics of the material and the solubility in aqueous media at pH > 5, while also maintaining the hydrophobicity degree of the polymeric surface.

Aerobic Biodegradation of Liquid Motor Fuels under Extreme Acidic Conditions

Biodegradation of liquid petroleum motor fuels and fuel mixtures containing biodiesel fuel (methyl ethers of rapeseed fatty acids) by aerobic acidophilic actinobacteria Mycobacterium sp. AGS10 was studied. Strain AGS10 was found to be able to grow on aviation kerosene Jet A-1 as the sole carbon and energy source under highly acidic conditions. After 21 days of cultivation at 30°C and pH 2.5, bacterial numbers increased from 4.2 × 106 to 7.0 × 108 cells/mL, while the hexane-soluble part of the fuel was degraded by 90.4%. The strain also utilized components of the winter diesel fuel, including С8–С20n-alkanes, iso-alkanes, and aromatic compounds. Overall hydrocarbon consumption under the same conditions was 99.4%. The ratio of (iso-С19 (pristane) + iso-С20 (phytane))/(n-С17 + n-С18) changed from 1.21 in the control to 2.39 in the experiment with bacterial degradation, which indicated preferable utilization of n-alkanes, rather than isoprenoids. Over 90% of diesel fuel hydrocarbons were consumed from day 4 to day 12 of cultivation, while abundance of the bacterial population increased by three orders of magnitude. Strain AGS10 consumed both hydrocarbons and oxygen-containing (plant-derived) components of the fuel mixtures with biodiesel fuel. Bacteria preferentially consumed hydrocarbons, and the ratio between oil diesel fuel and biodiesel fuel in the mixture changed in the course of incubation.

Extremely acidic environment: Biogeochemical effects on algal biofilms

The biological responses of acidobiontic species to extremely acidic waters, as those related with Acid Mine Drainage (AMD) processes, are relevant not only to understand the toxicological degree of the waters as well as the mechanisms responsible for the survival and adaptation of such organisms.Therefore, the objective of this study was to evaluate the effect of acidic pH and metals in biofilms collected in two sites a lentic permanent acid pond (AP) and a temporary acid stream (AS) affected by Acid Mine Drainage (AMD), and taking as control (C), an uncontaminated site with circumneutral pH. The results showed typical conditions of AMD-contaminated waters in sites AS and AP (pH < 3 and high concentrations of Al, Cu, Fe, Mn, Pb and Zn), which are responsible for a substantial decrease in biomass and biodiversity of biofilms (with a dominance of acidobiontic species, such as Pinnularia aljustrelica and Eunotia exigua, comparing to the control site. Also expressed by low values of photosynthetic pigments and reduced amount of proteins. In addition, such extreme acidic conditions also induced biofilms’ stress, increasing antioxidant [catalase (CAT), superoxide dismutase (SOD) and biotransformation glutathione S-transferases (GSTs)] enzymes activity and also membrane damage (peroxidized lipids). However, despite the quite similar physico-chemical conditions of both AMD-contaminated sites, differences in the toxicity status between them were indirectly detected through some of the biochemical parameters [GSTs, SOD and CAT], indicating site AS has the most toxic, which fact was attributed to the higher concentrations of Pb2+ in this water. This element is recognized to be highly toxic for biota, and in such acidic conditions remains in solution, easily available to the aquatic organisms. Since pH is similar in the acid sites, the different concentrations of heavy metals in the waters might be responsible for the observed changes in the biological community at these two sites.This fact was translated in a higher capacity of this site's biofilm to cope with the negative effects of the toxicants, evidenced in a higher positive correlation with GSTs, CAT and SOD when compared to biofilms of sites AP and C.

3D-Printed Anti-Fouling Cellulose Mesh for Highly Efficient Oil/Water Separation Applications.

The ability of additive manufacturing to print mesh structure was exploited to fabricate highly efficient filtration meshes for oil/water separation applications. Through Direct Ink Writing (DIW) technique, pure cellulose acetate with a mesh architecture can be created easily, using cellulose acetate/ethyl acetate solution as the ink and simply drying off the solvent in ambient conditions. Besides conventional mesh structures, more complex structures can be fabricated in order to manipulate the pore size and hence tune the separation properties of the mesh. The superhydrophilic 3D-printed cellulose meshes are able to achieve a high separation efficiency of >95% as long as the average pore size is smaller than 280 μm. More importantly, the mesh that possesses an unconventional complex structure boasts a separation efficiency of ∼99% while maintaining a high water flux of ∼160 000 Lm2-h-1. The 3D-printed cellulose meshes are also able to separate oil substances of a wide range of viscosity, from highly viscous PDMS (∼97 cP) to nonviscous cyclohexane (∼1 cP) and are chemically resistant to extreme acidic and alkaline conditions. Moreover, the 3D-printed cellulose meshes also possess antioil-fouling/self-cleaning ability, which makes its surfaces resilient to contamination. In addition, the 3D-printed meshes do not suffer from surface inhomogeneity and interfacial adhesion issues as compared to the usual coated meshes. Such a robust yet practical system is highly applicable for highly efficient oil-water separation applications.

Domestication of Local Microbial Consortia for Efficient Recovery of Gold Through Top-Down Selection in Airlift Bioreactors.

Extreme acidophiles play central roles in the geochemical cycling of diverse elements in low pH environments. This has been harnessed in biotechnologies such as biomining, where microorganisms facilitate the recovery of economically important metals such as gold. By generating both extreme acidity and a chemical oxidant (ferric iron) many species of prokaryotes that thrive in low pH environments not only catalyze mineral dissolution but also trigger both community and individual level adaptive changes. These changes vary in extent and direction depending on the ore mineralogy, water availability and local climate. The use of indigenous versus introduced microbial consortia in biomining practices is still a matter of debate. Yet, indigenous microbial consortia colonizing sulfidic ores that have been domesticated, i.e., selected for their ability to survive under specific polyextreme conditions, are claimed to outperform un-adapted foreign consortia. Despite this, little is known on the domestication of acidic microbial communities and the changes elicited in their members. In this study, high resolution targeted metagenomic techniques were used to analyze the changes occurring in the community structure of local microbial consortia acclimated to growing under extreme acidic conditions and adapted to endure the conditions imposed by the target mineral during biooxidation of a gold concentrate in an airlift reactor over a period of 2 years. The results indicated that operative conditions evolving through biooxidation of the mineral concentrate exerted strong selective pressures that, early on, purge biodiversity in favor of a few Acidithiobacillus spp. over other iron oxidizing acidophiles. Metagenomic analysis of the domesticated consortium present at the end of the adaptation experiment enabled reconstruction of the RVS1-MAG, a novel representative of Acidithiobacillus ferrooxidans from the Andacollo gold mineral district. Comparative genomic analysis performed with this genome draft revealed a net enrichment of gene functions related to heavy metal transport and stress management that are likely to play a significant role in adaptation and survival to adverse conditions experienced by these acidophiles during growth in presence of gold concentrates.

Direct electrochemical biosensing in gastrointestinal fluids.

Edible electrochemical biosensors with remarkable prolonged resistance to extreme acidic conditions are described for direct glucose sensing in gastrointestinal (GI) fluids of different pH ranges and compositions. Such direct and stable glucose monitoring is realized using carbon-paste biosensors prepared from edible materials, such as olive oil and activated charcoal, shown to protect the activity of the embedded glucose oxidase (GOx) enzyme from strongly acidic conditions. The enzymatic resistance to low-pH deactivation allowed performing direct glucose monitoring in strong acidic environments (pH1.5) over a 90-min period, while the response of conventional screen-printed (SP) biosensors decreased significantly following 10-min incubation in the same fluid. The developed edible biosensor displayed a linear response between 2 and 10mM glucose with sensitivity depending on the pH of the corresponding GI fluid. In addition, coating the electrode surface with pH-responsive enteric coatings (Eudragit® L100 and Eudragit® E PO), of different types and densities, allows tuning the sensor activation in gastric and intestinal fluids at specific predetermined times. The attractive characteristics and sensing performance of these edible electrochemical biosensors, along with their pH-responsive actuation, hold considerable promise for the development of ingestible devices towards the biosensing of diverse target analytes after prolonged incubation in challenging body fluids. Graphical Abstract Edible biosensors allow direct electrochemical sensing in different gastrointestinal fluids and display remarkable prolonged resistance to extreme acidic conditions.

Enhanced osteogenic differentiation of MC3T3-E1 on rhBMP-2 immobilized titanium surface through polymer-mediated electrostatic interaction

Titanium and its alloy are widely used in osteointegration. However, osteogenic activity requires enhancements in order to meet clinical needs. To enhance the osteogenic activity of titanium, human recombined bone morphogenetic protein 2 (rhBMP-2) was immobilized on a titanium surface through self-assembly driven by electrostatic interaction. Pure titanium foil (10 mm in diameter and 0.3 mm thickness) was coated with gold nanoparticles (TA) by magnetron sputtering, and then the gold dots were decorated with negatively charged polymer (TA/BPP) in order to generate positively charged rhBMP-2 complex (TA/BPP/BMP-2) on the surface. The surface characteristics and the bioactivity and osteogenic activity of the surface-modified titanium were detected.The results showed that rhBMP-2 was successfully complexed on the titanium surfaces. The zeta potential of TA surfaces decreased after contacting with BPP solutions but rebounded after rhBMP-2 coating. The loading efficiency of rhBMP-2 reached 83.4% ± 2.02%, and the amount of rhBMP-2 released at physiological pH conditions was minimum and increased at extreme acidic conditions. The osteogenic capability was significantly elevated when MC3T3-E1 cells were cultured on TA/BPP/BMP-2 rather than other surfaces.In conclusion, rhBMP-2 can be successfully immobilized on titanium surfaces by electrostatic adsorption using negative polymer, which results in enhanced bioactivity, osteogenic capability in vitro.

Crosslinked PVDF membranes for aqueous and extreme pH nanofiltration

Loose poly(vinylidene difluoride) nanofiltration membranes were crosslinked using a one-pot reaction with para-xylenediamine in alkaline conditions. The crosslinking reaction was characterized using ATR-FTIR and EDX-based elemental analysis as function of reaction time. Upon crosslinking, the retention of the membranes improved dramatically for rose Bengal (RB) (from 90% to 100%) and MO (from 49% to 91%) without significant loss of permeability. The physico-chemical changes of the membrane during the crosslinking reaction were further characterized through XRD, TGA, DSC and DMA. Crosslinking resulted in a strong decrease in crystallinity of the semi-crystalline PVDF and tensile strength and thermal stability. The 24 h crosslinked PVDF membranes were tested for NF application in extreme pH conditions. The membranes were found to be suitable in both extreme acidic and alkaline conditions (5 M HCl or NaOH). The RB retention was not affected at all by the extreme conditions. Although a small decrease in permeance was observed for the acid treated membrane, the permeance of the alkaline treated membrane was not affected. This proves that crosslinking is a suitable strategy to improve the stability of PVDF, especially in alkaline conditions where pristine PVDF is not applicable at all, and furthermore is a tool to decrease the MWCO.

PH-induced structural changes of apo-lactoferrin and implications for its function: a molecular dynamics simulation study

ABSTRACTThe minor protein in milk, lactoferrin (Lf), is known for a variety of biological functions, and has been investigated as a protective encapsulant for probiotic bacteria in health-promoting food products. Lf is likely to be exposed to extreme pH conditions which are known to have disruptive influences on its functionality. The molecular mechanisms underlying these pH-dependent changes are not well-understood. To explore the potential of Lf as an encapsulant, molecular dynamics (MD) simulations were applied to study its conformational changes under extreme acidic (pH 1.0) or basic (pH 14.0) conditions, relative to neutral pH. Simulations indicate that the structure of apo-Lf is relatively stable at neutral pH, while acidic and basic pH result in substantially greater flexibility, partly induced by the loss of contacts between the N- and C-terminal lobes, causing them to undergo extensive relative bending and twisting motions. Basic pH causes greater structural disruption compared to acidic exposure. The latter has greater influence on the N-terminus, with increased fluctuations and disruptions of inter-residue contacts compared to those at neutral pH; while basic pH was found to more prominently disrupt contacts at the C-terminus. These results help elucidate possible functional consequences on Lf of exposure to extreme pH conditions.

An efficient methodology for the purification of date palm peroxidase: Stability comparison with horseradish peroxidase (HRP).

In the present study, Peroxidase from date palm (Phoenix dactylifera) leaves was purified to homogeneity by three-step procedure including aqueous two-phase system, hydrophobic and Ion-exchange chromatography. The enzyme migrated as single band on SDS-PAGE giving molecular weight of 68 ± 3 kDa. The purification factor for purified date palm peroxidase was 68 with high 41% yield. Enzymatic assays together with far-UV circular dichroism (CD), intrinsic and extrinsic fluorescence studies were carried out to monitor the structural stability of date palm and horseradish peroxidase (HRP) against various pH and temperatures. Activity measurements illustrated different pH stability for date palm and HRP. Both peroxidases are more susceptible to extreme acidic conditions as suggested by 4 & 15 nm red shift in date palm and HRP, respectively. Secondary structure analysis using far UV-CD exhibited predominance of α-helical (43.8%) structure. Also, pH induces loss in the secondary structure of date palm peroxidase. Thermal stability analysis revealed date palm peroxidase is more stable in comparison to HRP. In summary, date palm peroxidases could be promising enzymes for various applications where extreme pH and temperature is required.